Efficiencies Of Breathing Through Nasal And Oral Routes In General Anesthesia Adult Human Subjects

Objective:As the benefit of mouth-to-mouth breathing (MMB) during adult cardiopulmonary resuscitation (CPR) was questioned and was suggested to delete for layperson CPR, we speculated if other ventilation mode can be more effective. We hypothesized that mouth-to-nose breathing (MNB) might insure a more patent airway and more effective ventilation than MMB during adult CPR. We tested this hypothesis by comparing1) the efficiencies of nasal mask ventilation and oral mask ventilation and2) efficiencies of actual MNB and MMB in non-paralyzed, apneic, adult subjects under general anesthesia.Methods:Adult subjects (n=48) requiring general anesthesia were enrolled in this study. The study was divided to two parts. Part One:Twenty-eight subjects received in random order nasal mask ventilation and oral mask ventilation in the head neutral position and Part Two:20different subjects received direct MMB and MNB in random order with the head in the neutral and extended position. The rate of effective ventilation and respiratory parameters were recorded simultaneously from both the nasal and oral masks or MNB and MMB.Results:All data is presented with mean±SD or median (inter-quartile ranges). Part one: The rates of effective ventilation (expired volume> estimated anatomic dead space) were100%(100-100%) for nasal mask ventilation vs.0%(0-100%) for oral mask ventilation (p<0.001). The peak inspiratory airway pressure during nasal ventilation (15.3±2.9cm H2O) was lower than that during oral ventilation (27.3±7.7cm H2O)(p<0.001). Effectiveness of ventilation (volume of CO2removed per breath/peak airway pressure) with nasal mask [0.3ml/cm H2O (0.2-0.6ml/cm H2O)] was higher than that with oral mask [0.0ml/cm H2O (0.0-0.3ml/cm H2O)](p=0.01). Part Two:During MNB vs. MMB regardless of head position, the rates of effective ventilation were91.1%(42.4-100%) vs.43.1%(42.5-100%)(p<0.001), inhaled tidal volume [136ml (43.5-355.5ml)] and expired tidal volume [130.5ml (44.0-372.8ml)] with MMB was significantly lower than that [320ml (141-533.5ml)] and [324.5ml (140.8-509.0ml)] with MNB respectively (p＜0.001). The rate of effective ventilation and expired tidal volume during MNB were significantly greater than those during MMB in head neutral position. There is no obvious difference of MNB and MMB in head extended position.Conclusion:Nasal route ventilation (nasal mask ventilation or MNB) is more effective than oral route (oral mask ventilation or MMB) in apneic, non-paralyzed, adult subjects undergoing general anesthesia. Additional studies are needed to establish whether using MNB during cardiopulmonary resuscitation will improve patient outcomes.